報錯總結：
1.場景：內網環境，開通上網條件，可以ping通www.baidu.com，但是有yum進行install會報錯
2.報錯如下：
One of the configured repositories failed (CentOS-7 - Addons - sohu.com), and yum doesn't have enough cached data to continue. At this point the only safe thing yum can do is fail. There are a few ways to work "fix" this:
\1. Contact the upstream for the repository and get them to fix the problem.
\2. Reconfigure the baseurl/etc. for the repository, to point to a working upstream. This is most often useful if you are using a newer distribution release than is supported by the repository (and the packages for the previous distribution release still work).
\3. Disable the repository, so yum won't use it by default. Yum will then just ignore the repository until you permanently enable it again or use --enablerepo for temporary usage:
yum-config-manager --disable addons
\4. Configure the failing repository to be skipped, if it is unavailable. Note that yum will try to contact the repo. when it runs most commands, so will have to try and fail each time (and thus. yum will be be much slower). If it is a very temporary problem though, this is often a nice compromise:
yum-config-manager --save --setopt=addons.skip_if_unavailable=true
failure: repodata/repomd.xml from addons: [Errno 256] No more mirrors to try.http://mirrors.aliyun.com/non-supported/rhel/7/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Foundhttp://mirrors.aliyun.com/non-supported/rhel/7/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found
3.報錯處理思路：
1.看網絡怎么樣，表現在可以ping通www.baidu.com,可以用wget下載文件（可以下載阿里的網絡源：）
CentOS7
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
CentOS6
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
2.網絡沒問題，那么就是你的repo庫有問題。文件在/etc/yum.repos.d/下面，一定會有要有一個網絡源（例如mirrors.aliyun.com）,還必須有個本地源及一個epel源，先將epel源刪了，然后yum clean all && yum makecache 3.可以把網絡源中的mirrors這一列注釋掉，留下baseurl，測試yum -y install gcc
4.上面還不行就把網絡源中baseurl也注釋掉，直接用本地源，測試yum -y install gcc